This invention relates to an improved mould system and method for the vertical continuous casting of molten metals, such as aluminum, to provide solidified circular cross section ingots for further processing into semi-fabricated metal products. More particularly, the invention relates to a mould apparatus for use in conjunction with a vertical, direct chill casting system for aluminum, magnesium and their alloys.
It is well known to those skilled in the art of direct chill casting that ingots of the highest surface and internal quality can be cast when the mould length is very short and precisely coordinated with the alloy, diameter and casting speed of each particular product it is desired to produce. This is shown, for example, in McCubbin U.S. Pat. No. 4,071,072. Only by using very short moulds of the order of 10-40 mm in length can the direct chill cooling effect be utilized to overcome the inevitable loss of ingot-mould contact which results from the formation of the air-gap.
There are a number of new mould designs based upon the above principles, which are equally capable of casting ingots of very high surface and internal quality. However, all of the new mould designs are characteristically complex in design, utilize expensive materials, must be built to close tolerances, and hence are relatively inflexible in terms of being able to cast high quality ingot only of the specific alloy and ingot diameter for which the mould is designed and constructed.
Unlike the casting of very large rectangular ingots, which are cast only in small numbers simultaneously, the major market for round cross-section ingots is in small to medium diameters, in the range of 125 to 250 mm. In order to obtain high productivity, large numbers of ingots, e.g. 24 to 96, must be cast simultaneously. Accordingly, mould inventory costs are very high for a plant producing a wide range of alloys and ingot diameters using the new generation moulds capable of casting very high quality ingot.
It is the object of the present invention to provide a simplified mould system which will be capable of casting very high quality ingots while greatly decreasing the cost of mould inventory.